This study is designed to develop an in vitro potency assay to replace the guinea pig death test portion of the official release test for the tetanus component in adsorbed toxoid vaccines. There has been no further investigation of the correlation between animal and laboratory tests this year due to problems with the supplies of reagents. In an informal collaboration with memnbers of DVP, this assay was modified to detect increases in Tetanus specific IgG in primates suspected to have lost the ability to respond to vaccination due to a possible tolerance effect. Serum samples taken before and after a single Tetanus immunization of several macaques were assayed. Substitution of an anti-human IgG conjugate indicated that the some of the animals had increased levels of Tetanus IgG, but sera from these animals failed to neutralize Tetanus Toxin in the traditional animal assay. Additional animals are being immunized, and potential future collaboration is being discussed.